Why mere presence of males shortens females` lifespans in some species

Washington: Researchers have discovered that males of the laboratory roundworm secrete signalling molecules that significantly shorten the lifespan of the opposite sex.

The scientists at the Stanford University School of Medicine speculated that, if carried out after reproduction, this "male-induced demise" could serve to conserve precious resources for a male`s offspring or to decrease the supply of mates for other males.

For several years, it`s been known that the presence of some male worms and flies can shorten the lifespan of their female or hermaphroditic counterparts. But it`s not been clear why. Some researchers have speculated that the physical stress of mating may lead to their early death.

The Stanford research, however, suggested something more than sex is to blame- specifically, that the males are carrying out a calculated plan at the molecular level to off the baby-makers after they`ve done their jobs.

"We`ve found that males induce the expression of a large number of genes involved in sensation and signalling in hermaphrodites," Anne Brunet, PhD, associate professor of genetics, said.

"This raises the possibility that the male-induced demise is not just due to the physical stress of copulation but instead involves some degree of active signalling. Indeed, we found that just placing hermaphrodites on plates where males had previously been present was sufficient to induce the premature demise of hermaphrodites," the researcher added.

The researchers found that the continuous presence of young males shortened the average lifespan of C. elegans hermaphrodites by more than 20 percent. This effect persisted even when the genders were prevented from co-mingling, or when the hermaphrodites were sterile- indicating that neither the physical stress of copulation nor the energy demands of producing offspring were entirely responsible for early death.